JP3781508B2 - Chip pad position detection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a chip pad position detecting method for wire bonding.
[0002]
[Prior art]
After a chip is mounted on a substrate such as a printed board or a lead frame by a die bonding apparatus, a chip pad and a substrate electrode are connected by a wire by a wire bonding apparatus.
[0003]
In wire bonding, a wire is bonded to a chip pad and a substrate electrode by causing the capillary tool through which the wire is inserted to move horizontally or vertically with respect to the chip or the substrate.
[0004]
A number of minute pads are formed on the upper surface of the chip with a narrow pitch, and the position of the pads must be determined accurately prior to wire bonding. Therefore, conventionally, the position of the pad of the chip has been obtained as follows.
[0005]
The first method is a method in which the chip pad is enlarged and displayed on the screen of a monitor television, and the operator obtains the position of the pad by aligning a cross-shaped cursor with the pad on the screen.
[0006]
The second method is a method of performing pattern matching using a CCD camera. Pattern matching uses the fact that there is a large luminance difference between the chip pad and its background, and obtains brightness (brightness and darkness) image data in the search area surrounding the pad, and the image data and master pattern image data are obtained. The position of the pad is obtained by matching.
[0007]
[Problems to be solved by the invention]
However, the first method has a problem that it takes a lot of time and labor because the operator manually determines the position of the pad by operating the cursor key.
[0008]
In the second method, the pad image captured by the CCD camera has (1) a lot of light and dark mottle, and (2) the corner that is the characteristic part of the pad is easily rounded. It is difficult to recognize clearly. (3) The lead of the circuit pattern is connected to the pad of the chip, and it is difficult to recognize the boundary between the pad and the lead. (4) The inspection device pressed for the quality inspection of the chip. There is a defect that the indentation of the probe is generated on the pad, and the indentation is likely to be noise. For this reason, there is a problem that the pattern matching accuracy is low and it is difficult to accurately determine the position of the pad. FIG. 6 shows a light / dark image diagram of a pad of a chip taken into a CCD camera for pattern matching. The pad 1 has a lot of mottle 2 and the corner 3 of the pad 1 It is rounded, and the circuit pattern lead 4 is connected to the pad 1, and the probe indentation 5 is present.
[0009]
Therefore, an object of the present invention is to provide a chip pad position detection method capable of accurately determining the position of a chip pad.
[0010]
[Means for Solving the Problems]
The chip pad position detection method of the present invention is a chip pad position detection method for detecting the position of a chip pad by capturing a chip image with a camera, and the chip pad in the image captured by the camera. A search area is set so as to surround the chip, and a first frame that is vertically long in the Y direction that crosses the pad of the chip in the X direction and a second frame that is horizontally long in the X direction that crosses in the Y direction are set inside the search area. The first frame and the second frame are moved in the X direction and the Y direction in the search area surrounding the pad, and the respective distributions are determined from the light / dark ratios in the first frame and the second frame. Next, the position of the edge in the X direction and the Y direction where the change rate of the light / dark ratio changes to a threshold value or more is obtained from the distribution, and the position of the pad is obtained from the position of the edge in the X direction and the Y direction. did.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention having the above-described configuration, if an edge at which the light / dark ratio changes more than a threshold value is obtained from the distribution of the light / dark ratio when the first frame and the second frame are moved in the X direction and the Y direction. Since it is good, even if the image quality of a pad is a little bad, the position can be calculated | required correctly.
[0012]
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view of a chip pad position detection device according to an embodiment of the present invention, FIG. 2 is an image view of a search area captured by the camera, and FIG. 3A is an X in the search area. FIG. 3B is an image view of the search area, FIG. 4 is a light-dark ratio distribution diagram in the Y direction in the search area, and FIG. 5 is a flowchart of pad position detection of the chip. is there.
[0013]
First, the configuration of the chip pad position detecting device will be described with reference to FIG. In FIG. 1, reference numeral 11 denotes a chip, and a large number of pads 12 are formed on the upper surface thereof. The chip 11 is mounted on the substrate 13. The pad 12 of the chip 11 and the electrode 14 of the substrate 13 are connected by a wire in a later process. Reference numeral 15 denotes a table for positioning the substrate 13.
[0014]
A camera 16 and a ring-shaped light source 17 are provided above the table 15. The camera 16 is a CCD camera. The camera 16 is held on the moving table 18, and when the moving table 18 is driven, the camera 16 moves horizontally in the X direction and the Y direction to recognize the pad 12 of the chip 11.
[0015]
The camera 16 is connected to an image storage unit 21 via an AD conversion unit 20, and the image processing unit 11 is connected to an inspection processing unit 22 including a CPU. The inspection processing unit 22 is connected to a storage unit 23 that stores various data and a display unit 24 such as a motor TV.
[0016]
Next, an image in the search area will be described with reference to FIG. In FIG. 2, S is a search area set in the image captured by the camera 16 and is set so as to surround the pad 12 of the chip 11. Inside the search area S, a vertically long first frame A in the Y direction and a horizontally long second frame B in the X direction are set. In FIG. 2, the image of the pad 12 is drawn as a clean square, but actually, the image has defects as described with reference to FIG. 6, and the image quality is considerably poor.
[0017]
Next, a method for detecting the position of the pad 12 of the chip 11 will be described with reference to the flowchart of FIG. First, the image of the chip 11 is captured by the camera 16 (step 1), and the binarization process is performed by the AD converter 20 (step 2). Next, as shown in FIG. 2, the first frame A is set so that the midpoint of the vertically long first frame A crosses the ideal position P of the pad 12 in the search area S (step 3). Next, the first frame A is moved in the X direction, and the distribution of the light / dark ratio in the first frame A in the search area S is obtained (step 4). FIG. 3A shows the distribution of the light / dark ratio in the X direction obtained in this way. Since the pad 12 reflects light specularly, the pad 12 is observed brightly, and the background of the pad 12 (background of the chip 11) absorbs light and is observed dark, so that the distribution of the light / dark ratio shown in FIG. It is done.
[0018]
Next, in steps 5 and 6, the second frame B is set so that the midpoint of the horizontally long second frame B crosses the ideal position P of the pad 12, and the inside of the search area S is moved in the Y direction. To obtain the distribution of the light / dark ratio. FIG. 4 shows the distribution of the light / dark ratio in the Y direction thus obtained.
[0019]
In FIG. 3A, the brightness ratio changes greatly at the edges E1 and E2 of the pad 12, so the positions of the edges E1 and E2 in the X direction are obtained as follows (step 7). That is, in FIG. 3A, first, a change rate ΔL (i) = | L (i) −L (i + 1) | (i = 1, 2, 3...) Of the light / dark ratio L is obtained. Next, a position where ΔL (i) exceeds the threshold value is obtained. In this example, there are six of x3 to x4, x4 to x5, x5 to x6, x12 to x13, x13 to x14, x14 to x15, x15 to x16.
[0020]
Next, from among the six, the X coordinate closest to the ideal position P of the pad 12 is obtained one by one in the front-rear direction. In this example, it is x6 and x12 as is clear from FIGS. From this, the X coordinate x6 of the edge E1 and the X coordinate x12 + W of the edge E2 are obtained. Here, W is the width of the first frame A.
[0021]
Similarly, edges E3 and E4 in the Y direction are obtained from FIG. 4 (step 8). The edges E1 to E4 can also be detected by differentiating the waveforms shown in FIGS. 3A and 4 and obtaining the positions of the waveforms obtained by the differentiation above the threshold value. The edges E1 to E4 may be obtained without being influenced by noise. Then, an X coordinate of the center of the pad 12 is obtained by obtaining an intermediate point between E1 and E2, and a Y coordinate position of the pad 12 is obtained by obtaining an intermediate point between E3 and E4 (step 9). Thus, the position of the pad 12 is obtained.
[0022]
【The invention's effect】
In the present invention, a vertically long first frame and a horizontally long second frame are set in the search area, and a light / dark distribution is obtained by moving in a direction crossing the pad, and a position where the light / dark ratio changes more than a threshold value is determined. Since the position of the edge is obtained, and the position of the pad is obtained from the position of the edge, the position of the edge is obtained even if the image quality of the bright and dark image of the pad taken into the camera is poor as shown in FIG. Is easily possible, so the position of the pad can be determined accurately.
[Brief description of the drawings]
FIG. 1 is a side view of a chip pad position detection device according to an embodiment of the present invention. FIG. 2 is a diagram showing a search area captured by a camera of a chip pad position detection device according to an embodiment of the present invention. FIG. 3A is a light / dark ratio distribution diagram in the X direction within the search area of the chip pad position detecting device according to the embodiment of the present invention. FIG. 3B is a chip pad according to the embodiment of the present invention. FIG. 4 is an image of a search area of a position detection apparatus of the present invention. FIG. 4 is a distribution diagram of brightness ratios in the Y direction in the search area of the position detection apparatus for a chip pad according to an embodiment of the present invention. Flowchart of chip pad position detection of chip pad position detection device in form of embodiment [FIG. 6] Bright and dark image diagram of chip pad taken in CCD camera
11 Chip 12 Pad 16 Camera A First frame B Second frame S Search area E1, E2, E3, E4 Edge

Claims (1)

A chip pad position detection method for detecting a chip pad position by capturing a chip image with a camera, setting a search area so as to surround the chip pad in the image captured by the camera, Inside this search area , a vertically long first frame is set in the Y direction that crosses the pad of the chip in the X direction, and a horizontally long second frame is set in the X direction that crosses in the Y direction. The first frame and the second frame are respectively moved in the X direction and the Y direction to obtain respective distributions from the light / dark ratios in the first frame and the second frame, and then the rate of change of the light / dark ratio from the distributions. A method for detecting a position of a pad on a chip, wherein the position of an edge in the X direction and the Y direction at which the value changes beyond a threshold value is obtained, and the position of the pad is obtained from the position of the edge in the X direction and the Y direction .

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